This invention relates to polychloroprene latex adhesive compositions. More specifically, this invention relates to polychloroprene adhesive compositions which are particularly suited to bonding foamed polymeric materials such as polyurethanes and polyolefins to substrates including bonded fibre board, thermoplastic olefins, fabric, and polyurethanes.
Polymers of chloroprene (i.e. 2-chloro-1,3-butadiene) are well known, commercially available elastomers useful in the manufacture of general rubber goods, adhesives, and coating compositions. They are especially suited for formulation of contact adhesives, which are generally sold in the form of cements, i.e. solutions of polymers and additives in organic solvents. Most commonly, the polychloroprenes used as elastomeric components in these cements are chloroprene homopolymers having relatively high levels of crystallinity. Such polymers promote rapid adhesive bond strength development, i.e. green bond strength, without the requirement of a further curing step. See R. M. Murray, et al., The Neoprenes, Elastomer Chemicals Department, E. I. du Pont de Nemours & Co. (1963), p.83.
A disadvantage of the use of highly crystalline chloroprene homopolymers, however, is that cements containing them are susceptible to bond failure at temperatures of, for example, 80.degree. C.-95.degree. C., unless a second curing step is employed. It is known that chloroprene copolymers generally exhibit excellent high temperature resistance. Despite this enhanced thermal resistance, merely substituting chloroprene copolymers for chloroprene homopolymers is not an acceptable means to solve the problem of temperature susceptibility of polychloroprene homopolymer cements. This is because chloroprene copolymers have inherently low crystallinity and therefore, adhesives containing these polymers exhibit inferior green bond strength. Thus, neither chloroprene homopolymer cements of the prior art nor chloroprene copolymer cements of the prior art combine outstanding high temperature resistance and green bond strength.
A further disadvantage of polychloroprene cements is that they usually contain large quantities of volatile organic solvents. Due to environmental concerns, and in view of the recognized safety hazards associated with organic solvents, the use of aqueous latex adhesives is more desirable than the use of solvent-based adhesives in many applications. There is thus a need in the art for improved polychloroprene adhesives which exhibit superior high temperature resistance coupled with green bond strength, yet which are environmentally safe.